The present invention generally relates to wall anchors, and more specifically to wall anchors for use in a wall composed of a friable material such as drywall or gypsum wallboard. Wall anchors are known in the art, and generally take the form of a friction-fit anchor, which is hammered into the wall, or a self-drilling anchor, which is screwed into the wall. These wall anchors are used to mount articles to a wall that is made with gypsum wallboard. The wall anchors are usually made of a rigid plastic or a metal such as zinc.
Conventional self-drilling anchors are available from ITW Buildex Division, Itasca, Illinois under the mark xe2x80x9cE-Z Anchorxe2x80x9d, and are disclosed in U.S. Pat. No. 4,601,625, which is incorporated by reference. Such self-drilling anchors are screwed into the wall by an installer using an insertion device such as a manual or powered Phillips-head screwdriver. Self-drilling anchors generally include three components: a flange which prevents the anchor from completely entering the wall and accepts the insertion device, a threaded portion on a generally tubular, cylindrical body that engages the friable material and draws the anchor into the wall, and a blade or drilling portion which drills or bores a hole into the friable material or substrate. Inside the cylindrical body is a central bore that accepts a threaded fastener, such as a screw into the anchor for mounting an article in place on the wall. Splines are usually disposed on the interior surface of the cylindrical body, extend longitudinally with respect to the body and engage the threaded fastener. The use of splines allows the threaded fastener to be relatively easily inserted into the wall anchor due to the small amount of contact surface area between the threaded fastener and the splines, and provides: secure mounting of the article to be mounted.
Upon installation of a fastener into the body, the drilling portion is caused to deflect laterally. This deflecting feature is beneficial in that it allows the use of a screw which has a predetermined length regardless of the thickness of the material being fastened. Also, in applications where the wallboard is installed against a hard surface such as concrete, the anchor is first threaded into the wallboard to create a hole. The installer then removes the anchor by counter-clockwise rotation, and manually breaks off the drilling portion. Next, the anchor is reinstalled into the wallboard. In this manner,. the broken off drilling portion does not become lodged between the wallboard and the wall, which would result in an unsatisfactory installation.
U.S. Pat. No. 5,558,479, to McElderry, which is incorporated by reference, discloses a wall anchor that has two types of splines disposed on the interior wall of the cylindrical body. A first type includes at least one spline protruding centrally at a narrow angle, and a second type including at least one spline protruding centrally at a wider angle. The different sized splines allow different sizes of fasteners to be inserted into the same sized wall anchor. When a #6 sheet metal screw (SMS) is inserted into the McElderry wall anchor, the first type of spline will primarily engage the threads of the #6 SMS. A relatively larger diameter #8 SMS can also be inserted into the McElderry wall anchor and both the first and second type of splines will engage the threads of the #8 SMS.
Prior art wall anchors have a problem of xe2x80x9cwalkingxe2x80x9d, which refers to the anchor being screwed into the wall off-line, and are also relatively slow to install due to the relatively dull structure of their drilling portions. These drawbacks are generally more evident when the anchors are made of plastic rather than metal. Another problem that exists with the prior art anchors is that they generate gypsum dust or powder when being drilled into the drywall. In most cases, this dust or powder is ejected from the hole into which the anchor is being drilled, and leaves a messy residue. Further, the prior art wall anchors tear and rip the drywall paper.
It is therefore an object of the present invention to provide an improved wall anchor with a new sharp drill point which starts drilling faster and will not walk during installation.
Another object of the present invention is to provide an improved w all anchor with cutting edges or blades on the drill point which cut and remove gypsum faster during installation.
Still another object of the present invention is to provide an improved wall anchor with a stronger blade on the drill point which provides extra torsional strength.
A further object of the present invention is to provide an improved wall anchor with a new drill point design which reduces the amount of gypsum dust or powder ejected from the hole during drilling.
Yet another object of the present invention is to provide an improved wall anchor with a new drill point that cuts a clean hole in the drywall, resulting in less paper damage.
The abovexe2x80x94identified objects are met or exceeded by the present wall anchor, which features an improved drilling tip. Being relatively shorter and sharper than conventional self drilling anchor tips, the present tip drills faster and more accurately. Thus, unwanted xe2x80x9cwalkingxe2x80x9d is minimized. In addition, the present anchor generates less gypsum dust, resulting in a cleaner installation. Also, the relatively shorter tip has greater tortional strength than self conventional drilling anchors.
More specifically, the present wall anchor is for use in a friable material, and includes a generally cylindrical body having a flanged end, a central portion, and a drill end. The drill end has a generally flat blade including a first portion and a second portion. The first portion has a first angled cutting edge and a first side cutting edge, and the second portion has a second angled cutting edge and a second side cutting edge. These portions are formed on a common line and are offset relative to each other along a plane passing through a diameter of the cylindrical body. The central portion and the flange end have a combined axial length, and the drill end has an axial length which is shorter than that of the central portion and the flange end.